Hormonal Control of Growth Flashcards
Where is growth hormone produced, and what receptor does it activate?
The most abundant hormone produced in the adenohypophysis
It binds GH-R - JAk-STAT pathway.
What are the effects (two groups) of GH?
Directly activates growth - burn fat, protein synthesis
- Increased protein synthesis
- Increased AA uptake
- Increased lipolysis
- Reduce glucose uptake and increased gluconeogenesis
Increases IGF
- Increases IGF production in liver
- IGF is mitogenic (makes cells divide) and hypertrophic (makes muscle cells bigger)
What three general stimuli cause GHRH release from hypothalamus?
- Protein starvation
- Exercise
- Sleep
Why would starvation increase growth hormone release?
Particular type of starvation - protein starvation.
GH helps survive prolonged protein starvation by switching metabolism away from proetins as a fuel source.
What does IGF do and where is it produced?
GH stimulates increased production of IGF from:
- Liver - 75% of IGF-1
- Tissue specific IGF: Muscle, bone, heart
IGF Function:
- Stimulate AA uptake and protein synthesis
- Mitogenic and hypertrophic
- Resembles insulin in CHO metabolism regulation
What are the two isoforms of IGF?
IGF-1 = adult form
IGF-2 = fetal form
What is the relationship between
What is the relationship between GH, IGF and insulin?
GH cannot increase IGF levells in the absence of insulin,
Normal growth requires normal levels of insulin and GH to increase IGF-1.
What two syndromes can occur as a result of over-secretion of GH?
Before puberty - Gigantism
After puberty - Acromegaly (thickening of bones of hands/feet, loss of nerve function due to excessive bone/tendon growth, HTN)
What does under-secretion of GH cause before and after puberty?
Before - Dwarfism
After - little symptoms
What can cause reduced pituitary GH output?
Tumours - over-secretion of somatostatin
Infection - somatostatin secretion
Irradiation - GH secretion compromised
Uses of growth promoters
- Food production (e.g. horses)
- GH replacement treatment
- Sport (hGH)
